nervous system 3 - action potentials Flashcards
different phases of the action potential
1 - resting potential
2 - rising phase (depolarise)
3 - falling phase (repolarise)
4 - undershoot (more hyperpolarised)
voltage gated sodium channel
closed at rest (-65mV).
depolarisation to -40mV causes conformational change, opening pore
Na+ moves across conc gradient into cell, depolarises as positive ions entering negative side of membrane
when do all sodium channels open
-40mV
inactivated state vs closed state on voltage-gated Na+ channels
inactivated - ‘gate’ blocks open channel
closed - after inactivated, channel fully closes
what happens at peak depolarisation
Na+ channels close
voltage gated K+ channels during action potential
closed at rest. require depolarisation to open. delay (1ms) in open. allow hyperpolarisation.
what is the time where and excitable cell is unable to generate a subsequent action potential - two types?
refractory period:
absolute refractory period
relative refractory period (action potential chance lower due to hyperpolarisation)
what channels are open at point 3 - just after peak depolarisation where repolarisation begins
Na+ channels inactivate
K+ channels open
where is there a high concentration of sodium channels
axon initial segment
what influences conduction velocity
resistance of membrane - less resistance on larger axons
sodium channel density
what is the name for action potential propagation along myelinated axons
saltatory conduction
what are the gaps between myelin sheaths
nodes of ranvier
where are ion channels in myelinated axons?
very few under myelin, high concentrations in nodes of Ranvier
why can myelinated axons produce more efficient action potential propagation
node-to-node communication like a domino effect. passive depolarisation to next node opens Na+ channels on node 2
largest diameter myelinate axons- name and function
A-alpha
proprioceptors of skeletal muscle
second largest diameter myelinated axons- name and function
A-beta
mechanoreceptors of skin
smallest diameter myelinated axons- name and function
A-delta
pain, temperature
smallest unmyelinated axons - name and function
C
temperature, pain, itch
stretch, bend or pressure sensitive unmyelinated fibres?
mechanoreceptors
gating which depends on stretch of surrounding membrane?
mechanosensitive ion channels
name for areas of skin that tile the surface of the body linking specific areas of the skin with specific spinal nerves
dermatomes
amino acid neurotransmitters examples
glutamate (excitatory)
aspartate (inhibitory)
main neurotransmitters found in CNS
monoamines neurotransmitters examples
dopamine, noradrenaline, adrenaline, histamine, serotonin
all classes of neurotransmitters
amino acids
monoamines
peptides
others (e.g. acetylcholine)
synthesis and storage of neurotransmitters
enzymes synthesised in cell body, transported along axon, synthesise neurotransmitters, pack into vesicles, neurotransmitter released into synaptic cleft, component parts after breakdown taken up into presynaptic terminal, enzyme synthesises back into neurotransmitter.
which channels are present in pre- synaptic terminal
voltage gated calcium channels
sequence of events leading up to neurotransmitter release?
action potential reaches presynaptic terminal depolarising membrane and opening voltage gated calcium channels, vesicles bind to Ca2+ channels then release neurotransmitters
vesicles cycle
vesicle binds to membrane, Ca2+ entry triggers fusion of vesicle (exocytosis), new vesicle membrane pinched off, forms new vesicle and is filled with neurotransmitters again.
fast response post synaptic receptors?
ionotropic receptor. ion channels open when neurotransmitter binds
slow response post synaptic receptors
metabotropic receptors. activation of a second messenger
neurotransmitter binding activates G-protein, alpha subunit of G protein translocates and interacts with something else
what determines whether a synapse is excitatory or inhibitory
which neurotransmitter is released
effect of excitatory/inhibitory neurotransmitters
excitatory - depolarise towards threshold
inhibitory - hyperpolarise away from threshold
which channels open in inhibitory postsynaptic control (IPSP)
chloride (which is negative therefore more hyperpolarised, further from threshold)
convergence of synaptic inputs?
tens to thousands of presynaptic neurons input into one neuron
spacial summation?
summation of EPSPs generated at different synapses
temporal summation?
summation of EPSPs generated at same synapse
what does EPSP stand for? which channels open?
excitatory post synaptic potential. Na+ channels
what happens when there is an inhibitory input closer to the soma than an excitatory input on the same dendrite
inhibitory suppresses exhibitory
agonist vs antagonist
agonist - mimics effect of endogenous neurotransmitter
antagonist - blocks effect of endogenous neurotransmitter
what can mimic GABA
ethanol
barbiturates
neurosteriods
